The present invention relates to peak or expiratory flow meters for measuring the maximum exhalation flow rate of a patient.
A peak flow meter is a good general indicator of the presence or absence of airway obstruction and will determine the responsiveness of a patient to bronco dialaters. It is also known that airway obstruction associated with lung diseases is measurable long before symptoms may appear. The measurement of peak expiratory flow is one medical tool for the effective screening of presumably normal subjects away from the hospital and physician's office. Such a device would be particularly useful in factories and as part of health survey programs if an inexpensive peak flow meter was available. In the case of lung diseases, it is particularly important to determine the effectiveness of a prescribed drug without the necessity for hospitalization or constant visits to the physician's office and a peak flow meter may be indicative of the severity of an asthmatic attack.
In the past, expiratory flow meters have frequently been cumbersome or have a complexity of operation prohibiting home use or have lacked sufficient accuracy to be used as a medical screening tool. Frequently, prior art devices do not have a means for holding the peak flow reading, so that it is difficult for a patient to get an accurate reading without someone else watching the meter.
Typically, peak flow meters operate by lifting a ball, cylinder disc, or piston in a tube, which ball is raised by the patient exhaling into the tube to raise the ball. Most such devices do not have provisions for holding the readings of holding the ball at its maximum raised point. Another commonly suggested technique is to have a patient exhale through a passageway having a piston partially blocking the passageway and connected to a spring. This type of device requires special calibration, since the movement of the piston extends or compresses the spring and the force required to extend or compress the spring further is nonlinearly increased. In addition, springs tend to change over a period of time, thereby reducing the accuracy of the measurement.
The present invention is directed towards producing a simplified peak flow meter which can accurately measure the peak expiratory flow of a patient and which can hold the measurement until returned by the patient. Advantageously, the present invention can be used as a pulmonary achievement trainer for patients to practice exhaling into the peak flow meter.